U.S. patent application number 14/445323 was filed with the patent office on 2015-02-05 for methods and apparatus providing a substrate having a coating with an elastic modulus gradient.
The applicant listed for this patent is CORNING INCORPORATED. Invention is credited to Zhanjun Gao, Guangli Hu, Ralph Edward Truitt.
Application Number | 20150037554 14/445323 |
Document ID | / |
Family ID | 51352824 |
Filed Date | 2015-02-05 |
United States Patent
Application |
20150037554 |
Kind Code |
A1 |
Gao; Zhanjun ; et
al. |
February 5, 2015 |
Methods and Apparatus Providing a Substrate Having a Coating with
an Elastic Modulus Gradient
Abstract
Methods and apparatus are provide for: a substrate having first
and second opposing surfaces, and an elastic modulus; and layer(s)
having a thickness between first and second opposing surfaces
thereof, the first surface of the layer contacting the second
surface of the substrate, forming an interface. The layer may
exhibit one or more of: a first elastic modulus proximate to the
first surface thereof and a second elastic modulus proximate to the
second surface thereof, the second elastic modulus being
substantially higher than the elastic modulus value, the first
elastic modulus being lower than the elastic modulus of the
substrate, the second elastic modulus being higher than the elastic
modulus of the substrate, and the layer exhibiting an increasing
elastic modulus gradient through the thickness thereof from the
first elastic modulus to the second elastic modulus.
Inventors: |
Gao; Zhanjun; (Rochester,
NY) ; Hu; Guangli; (Horsebeads, NY) ; Truitt;
Ralph Edward; (Painted Post, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CORNING INCORPORATED |
Corning |
NY |
US |
|
|
Family ID: |
51352824 |
Appl. No.: |
14/445323 |
Filed: |
July 29, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61861121 |
Aug 1, 2013 |
|
|
|
Current U.S.
Class: |
428/217 |
Current CPC
Class: |
C03C 17/22 20130101;
Y10T 428/24983 20150115; C03C 17/225 20130101; C03C 2217/948
20130101; C03C 2217/91 20130101; C03C 17/23 20130101; C03C 2217/231
20130101 |
Class at
Publication: |
428/217 |
International
Class: |
C03C 17/22 20060101
C03C017/22 |
Claims
1. An apparatus, comprising: a substrate having first and second
opposing surfaces, and an elastic modulus; and at least one layer
having a thickness between first and second opposing surfaces
thereof, where the first surface of the layer contacts the second
surface of the substrate thereby forming an interface, wherein: (i)
the layer exhibits a first elastic modulus proximate to the first
surface thereof and a second elastic modulus proximate to the
second surface thereof, (ii) the second elastic modulus is
substantially higher than the first elastic modulus, (iii) the
first elastic modulus is lower than the elastic modulus of the
substrate, (iv) the second elastic modulus is higher than the
elastic modulus of the substrate, and (v) the layer exhibits an
increasing elastic modulus gradient through the thickness thereof
from the first elastic modulus to the second elastic modulus.
2. The apparatus of claim 1, wherein the elastic modulus gradient
of the at least one layer increases monotonically through the
thickness thereof from the first elastic modulus to the second
elastic modulus.
3. The apparatus of claim 2, wherein the layer is formed from a
single layer of material.
4. The apparatus of claim 2, wherein the layer is formed from a
plurality of discrete sub-layers of material, one atop the
other.
5. The apparatus of claim 4, wherein at least some adjacent layers
of the plurality of discrete sub-layers of material have differing
elastic moduli.
6. The apparatus of claim 4, wherein each of the plurality of
discrete sub-layers of material have differing elastic moduli.
7. The apparatus of claim 1, wherein the elastic modulus gradient
of the at least one layer increases discretely through the
thickness thereof from the first elastic modulus to the second
elastic modulus.
8. The apparatus of claim 1, wherein the first elastic modulus of
the layer is one of: (i) about 1-85% lower than the elastic modulus
of the substrate; (ii) about 5-70% lower than the elastic modulus
of the substrate; and (iii) about 10%-30% lower than the elastic
modulus of the substrate.
9. The apparatus of claim 1, wherein the first elastic modulus of
the layer is one of: (i) about 1-60 GPa lower than the elastic
modulus of the substrate; (ii) about 3-50 GPa lower than the
elastic modulus of the substrate; and (iii) about 7-20 GPa lower
than the elastic modulus of the substrate.
10. The apparatus of claim 1, wherein the second elastic modulus of
the layer is one of: (i) at least about 25% higher than the elastic
modulus of the substrate; (ii) between about 50-200% higher than
the elastic modulus of the substrate; (iii) about 100% higher than
the elastic modulus of the substrate; and (iv) at least about 200%
higher than the elastic modulus of the substrate.
11. The apparatus of claim 1, wherein the second elastic modulus of
the layer is one of: (i) at least about 15-20 GPa higher than the
elastic modulus of the substrate; (ii) between about 20-70 GPa
higher than the elastic modulus of the substrate; (iii) about 70
GPa higher than the elastic modulus of the substrate; and (iv) at
least about 140 GPa higher than the elastic modulus of the
substrate.
12. The apparatus of claim 1, wherein a magnitude of the difference
between the first and second elastic moduli of the layer is one of:
(i) at least about 25%; (ii) at least about 50%; (iii) at least
about 100%; and (iii) at least about 200%.
13. The apparatus of claim 1, wherein a magnitude of the difference
between the first and second elastic moduli of the layer is one of:
(i) at least about 15-20 GPa; (ii) at least about 30-40 GPa; (iii)
at least about 50-60 GPa; and (iii) at least about 70 GPa.
14. The apparatus of claim 1, wherein the substrate is formed from
at least one of quartz, glass, glass-ceramic, oxide glass, ion
exchanged glass, and combinations thereof.
15. The apparatus of claim 1, wherein the at least one layer is
formed from an inorganic material.
16. The apparatus of claim 1, wherein the at least one layer is
formed from at least one of: Indium-Tin-Oxide (ITO), aluminum doped
zinc oxide, gallium doped zinc oxide, fluorine doped tin oxide,
Al.sub.2O.sub.3, AlON, TiN, TiC, SiO.sub.2, TiO.sub.2,
Nb.sub.2O.sub.5, Ta.sub.2O.sub.5, SiO.sub.XN.sub.Y,
SiAl.sub.xO.sub.yN.sub.z, AlO.sub.xN.sub.y, SiN.sub.X, AlN.sub.x,
and TiN.sub.X, highly siliceous polymers, highly cured siloxane,
highly cured silsesquioxanes, and metal film.
17. The apparatus of claim 1, wherein the thickness of the at least
one layer is one of: (i) between about 50-10,000 nm; (ii) between
about 500-10,000 nm; (iii) between about 1000-2000 nm; (iv) between
about 10-200 nm; (v) between about 20-100 nm; (vi) between about
30-90 nm.
18. An apparatus, comprising: a substrate formed from at least one
of quartz, glass, glass-ceramic, oxide glass, ion exchanged glass,
and combinations thereof, having first and second opposing
surfaces, and an elastic modulus of between about 30-100 GPa; and
at least one layer having a thickness between first and second
opposing surfaces thereof, where the first surface of the layer
contacts the second surface of the substrate thereby forming an
interface, wherein: (i) the layer exhibits a first elastic modulus
proximate to the first surface thereof and a second elastic modulus
proximate to the second surface thereof, (ii) the first elastic
modulus is at least between about 1-65 GPa lower than the elastic
modulus of the substrate, and (iii) the layer exhibits an
increasing elastic modulus gradient through the thickness thereof
from the first elastic modulus to the second elastic modulus.
19. A method of making the apparatus of claim 1, by applying the
one or more layers onto the substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn.119 of U.S. Provisional Application Ser. No.
61/861,121 filed on Aug. 1, 2013, the content of which is relied
upon and incorporated herein by reference in its entirety.
BACKGROUND
[0002] The present disclosure relates to methods and apparatus for
achieving a functional coating on a substrate, where the coating
exhibits an elastic modulus gradient through a thickness
thereof.
[0003] Many consumer and commercial products employ a sheet of
high-quality cover glass to, for example, protect critical devices
within the product, provide a user interface for input and/or
display, and/or many other functions. For example, mobile devices,
such as smart phones, mp3 players, computer tablets, etc., often
employ one or more sheets of high strength glass on the product to
both protect the product and achieve the aforementioned user
interface. In such applications, as well as others, the glass may
be durable (e.g., scratch resistant and fracture resistant),
transparent, and/or antireflective. Indeed, in a smart phone and/or
tablet application, the cover glass is often the primary interface
for user input and display, which means that the cover glass would
exhibit high durability and high optical performance
characteristics.
[0004] Among the evidence that the cover glass on a product may
manifest exposure to harsh operating conditions, scratches are
probably the most common. Such evidence suggests that sharp
contact, single-event damage is the primary source of visible
scratches on cover glass in mobile products. Once a significant
scratch mars the cover glass of a user input/display element, the
appearance of the product is degraded and the resultant increase in
light scattering may cause significant reduction in brightness,
clarity and contrast of images on the display. Significant
scratches can also affect the accuracy and reliability of touch
sensitive displays. As a single severe scratch, and/or a number of
moderate scratches, are both unsightly and can significantly affect
product performance, they are often the leading complaint of
customers, especially for mobile devices such as smart phones
and/or tablets.
[0005] Accordingly, there are needs in the art for new methods and
apparatus for achieving functional coatings on substrates,
especially glass substrates.
SUMMARY
[0006] It may be advantageous to impart any number of functional
properties to a substrate, such as a glass substrate by applying a
coating to the substrate. The coating forms a layer(s) on the
substrate and such a substrate may be referred to herein as a
coated substrate. Although the advantageous functional properties
achieved by adding a layer to a substrate are numerous, one such
functional property is scratch resistance. In general, harder
surfaces exhibit better scratch resistance as compared with softer
surfaces (i.e., surfaces with reduced hardness). However, a given
substrate composition employed to achieve certain strength and
optical characteristics for a particular application may not
exhibit a desired level of hardness, and therefore a desired level
of scratch resistance.
[0007] For example, an oxide glass, such as Gorilla.RTM. Glass,
which is available from Corning Incorporated, has been widely used
in consumer electronics products. Such glass is used in
applications where the strength of conventional glass is
insufficient to achieve desired performance levels. Strengthened
glass, such as Gorilla.RTM. Glass, is manufactured by chemical
strengthening (e.g., via an ion exchange process) in order to
achieve high levels of strength while maintaining desirable optical
characteristics (such as high transmission, low reflectivity, and
suitable refractive index). Strengthened glass through ion exchange
(IX) techniques can produce high levels of compressive stress in
the treated glass, for example, as high as about 400 to 1000 MPa at
the surface. In addition, the ion-exchange depth of layer (or the
depth within the glass at which the ion exchange occurs) may be in
the range of about 15-100 microns. Where scratch resistance is
imparted, a desirable combination of hardness and elastic modulus
for Gorilla.RTM. Glass for applications in which scratch resistance
is of concern is on the order of about 15 GPa and higher hardness
and/or about 80 GPa or higher elastic modulus.
[0008] For purposes herein, the term "hardness" is intended to
refer to the Berkovich hardness test, which is measured in GPa and
employs a nano-indenter tip used for testing the indentation
hardness of a material. Also, for purposes herein, the phrase
"elastic modulus" is intended to refer to the Young's Modulus,
which may also be measured in GPa.
[0009] One approach to imparting one or more functional properties
to a given substrate, whether glass or otherwise, is to apply a
coating to the substrate to produce a composite structure that
exhibits such one or more functional properties. Where scratch
resistance is desired, the substrate may be combined with a layer
having a requisite hardness. For example, assuming that cost is not
a factor, a diamond-like carbon coating may be applied to a
substrate to improve hardness characteristics of the composite
structure. Indeed, diamond exhibits a hardness of 100 GPa. While
the addition of a coating atop a substrate may overcome inherent
limitations of a given substrate material, the coating may degrade
other characteristics of the substrate, such as the fracture
strength of the substrate and/or optical characteristics
thereof.
[0010] Through proper consideration of certain parameters of the
elastic modulus of the coating, a very satisfactory outer surface
having one or more desired functional properties may be achieved
without significantly diminishing the fracture strength of the
glass substrate. For example, one or more aspects may involve
providing a scratch resistant coating having a requisite hardness
on a substrate, where the coating exhibits an elastic modulus
gradient (i.e., wherein the coating has an elastic property that
varies through the thickness of the coating). In such aspects, the
coating imparts the desired functional property (i.e., scratch
resistance) without degrading the strength of the underlying
substrate. In general, an outer surface of the coating has a higher
elastic modulus than the glass substrate. The elastic modulus of
the coating reduces from the level at the outer surface through the
thickness of the coating to a value at the interface that is lower
than that of the substrate. In this way, the outer portion
(including the outer surface) of the coating is stiff (i.e.,
exhibits high elastic modulus), while the low elastic modulus at
the interface inhibits any driving forces from causing cracks to
penetrate into the substrate from the coating. Therefore, the
fracture strength of the substrate is maintained whilst
simultaneously improving the scratch resistance thereof. Likewise,
where other functional properties are desired, a coating exhibiting
such functional properties may be applied and may have an elastic
modulus gradient as described above.
[0011] As discussed above, the functional property of scratch
resistance may be imparted to a substrate by applying a hard
coating on the substrate. Similarly, a coating having other
attributes may be applied to the substrate to impart other function
properties, as described herein. For example, other functional
properties may be imparted to a substrate by coating same with a
layer of indium-tin-oxide ("ITO") or another transparent conductive
oxide (e.g., aluminum and gallium doped zinc oxides, fluorine doped
tin oxide, etc.) layers. For example, a conductive oxide layer may
be useful in producing touch screen displays. Still further
functional properties may be imparted to a substrate by applying a
coating of other materials to dispose IR or UV reflecting layers,
conducting or semiconducting layers, electronics layers,
thin-film-transistor layers, or anti-reflection ("AR") layers
(e.g., SiO2 and TiO2 layered structures) on the substrate.
[0012] Other aspects, features, and advantages will be apparent to
one skilled in the art from the description herein taken in
conjunction with the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
[0013] For the purposes of illustration, one or more embodiments
are shown in the drawings, it being understood, however, that the
embodiments disclosed and described herein are not limited to the
precise arrangements and instrumentalities shown.
[0014] FIG. 1 is a schematic view of a glass substrate coated with
a layer of material;
[0015] FIG. 2 is a graph illustrating a number of plots of
normalized energy release rate as a function of normalized crack
depth for respective coated substrates;
[0016] FIG. 3 is a schematic, side view of the coated glass
substrate of FIG. 1 taken through cross-sectional line 2-2;
[0017] FIG. 4 is a schematic view of the glass substrate being
subject to a coating process in order to form at least one layer
thereon;
[0018] FIG. 5 is a schematic, side view of an alternative
embodiment of the coated glass substrate of FIG. 1 taken through
cross-sectional line 2-2; and
[0019] FIG. 6 is a graphical representation of the fracture
strength of a number of substrates, both coated and non-coated,
illustrating the effect of such coating.
DETAILED DESCRIPTION
[0020] Various embodiments disclosed herein are directed to
improving one or more functional properties (e.g., scratch
resistance and/or other durability characteristics, such as
hardness, etc.) of a substrate, such as a glass substrate, by
applying one or more coatings onto the substrate. In order to
provide a fuller understanding of how the discoveries herein were
achieved, and therefore the broad scope of the contemplated
embodiments, a discussion of certain experimentation and/or theory
will be provided. It is noted, however, that the embodiments herein
are not necessarily limited to any such experimentation and/or
theory.
General Structure and Considerations
[0021] With reference to FIG. 1, a structure 100 may include a
substrate 102 of interest in connection with the development of
novel processes and structures to improve the mechanical properties
of the substrate 102. For example, the substrate 102 material may
be glass, strengthened glass, such as, specifically Gorilla.RTM.
Glass from Corning Incorporated, which is an ion-exchange glass,
usually an alkali aluminosilicate glass or alkali
aluminoborosilicate glass. Those skilled in the art will appreciate
that the specific substrate material is not limited to glass,
strengthened glass or Gorilla.RTM. Glass in particular, however,
such material was selected for experimentation and example. A bare
substrate 102 of Gorilla.RTM. Glass may exhibit an elastic modulus
of about 70 GPa and a hardness of about 7 GPa. A desirable
characteristic for scratch resistance (and/or other applications)
is on the order of at least about 80 GPa elastic modulus and/or at
least about 13 GPa hardness.
[0022] As mentioned above, the addition of a hard coating on the
substrate 102 may improve the scratch resistance of the structure
100; however, the coating also may reduce the fracture strength of
the substrate 102. A reason for the reduction in fracture strength
is attributable to differences in certain mechanical properties of
the coating versus certain mechanical properties of the substrate
102. For example, under load, a hard, brittle coating (such as
indium tin oxide (ITO)) can develop through-coating-cracks, such as
when the coating bends during a ring-on-ring fracture test of the
structure 100. These cracks develop before any flaws in the glass
substrate 102 begin to develop into cracks. As the load continues
to increase, the brittle nature of the coating results in the
release of stored energy at an energy release rate that is a
function of the mechanical properties of the coating material and
the mechanical properties of the substrate 102 material.
[0023] FIG. 2 is a graph illustrating a number of plots, each
representing the normalized energy release rate according to a
particular difference between the elastic moduli of the coating and
the elastic modulus of the substrate 102 for respective structures
100. Such effects have been considered in the literature, for
example, see, Beuth, J. (1992). Cracking of thin bonded films in
residual tension. Int J. Solid Structures, 29, No. 13, P1657-1675.
The ordinate (Y-axis) of the plot is the normalized energy release
rate, while the abscissa (X-axis) of the plot is the normalized
crack depth in the coating. The numeric label (alpha) of each plot
may be expressed as follows:
alpha=(E1-E2)/(E1+E2),
where Ei=E/(1-vi 2), i=1 denotes the properties of the coating, i=2
denotes the properties of the substrate 102, E is the Young's
Modulus, and vi is the Poisson's Ratio.
[0024] With reference to the plots of FIG. 2, when alpha is equal
to zero there is no mismatch because the coating and the substrate
102 have the same Young's modulus and Poisson's ratio.
Consequently, there is a relatively low energy release rate as a
crack approaches the interface of the coating and the substrate 102
(i.e., where the abscissa is equal to 1). When alpha is less than
zero, there is a mismatch because the Young's modulus of the
coating is less than the Young's modulus of the substrate 102.
Consequently, there is an even lower energy release rate as a crack
approaches the interface of the coating and the substrate 102.
Finally, when alpha is larger than zero, there is also a mismatch
because the Young's modulus of the coating is higher than the
Young's modulus of the substrate 102. Consequently, there is a
marked increase in the energy release rate as a crack approaches
the interface of the coating and the substrate 102. Indeed, the
higher the mismatch in Young's moduli of the substrate 102 and
coatings with higher Young's modulus than the substrate 102,
respectively, the higher the energy release rate will be at the
interface and the more prevalent the propagation of cracks will be
from the coating into the substrate 102. On the other hand, the
higher the mismatch in Young's moduli of the substrate and coatings
with higher Young's modulus than the substrate 102, respectively,
the lower the energy release rate will be at the interface and the
less prevalent the propagation of cracks will be from the coating
into the substrate 102. Indeed, under such circumstances a crack in
the coating tends to be interrupted at the interface and no
propagation into the substrate 102 occurs.
Desirable Characteristics--Gradient
[0025] With reference to FIG. 3, one or more embodiments herein
provide for a structure 100 having a substrate 102 and a layer 104
disposed on the substrate 102. In a broad aspect, the structure 100
includes the substrate 102 having first surface (not shown) and
second, opposing surface 106, and at least one layer 104
substantially covering the substrate 102. It is noted that the
phrase "substantially covering" herein means that the superior
layer (i.e., the layer 104) overlies the inferior layer (i.e., the
substrate 102) either directly or indirectly through one or more
intermediate layers. In one or more embodiments, the layer 104 may
be disposed on either or both sides of the substrate 102. In the
embodiment illustrated in FIG. 3, there are no intermediate layers
shown between, for example, the layer 104 and the substrate 102,
although such intermediate layers are contemplated. In a specific
embodiment, the at least one layer 104 has a thickness between a
first surface 104-1 and an opposing second surface 104-2 thereof,
where the first surface 104-1 of the layer 104 contacts the second
surface 106 of the substrate thereby forming an interface.
[0026] In one or more embodiments, the layer 104 is a protective
layer exhibiting scratch resistant characteristics. In one or more
alternative embodiments, the layer 104 may provide additional
and/or alternative functional properties, as otherwise described
herein. In this regard, the substrate 102 has a particular elastic
modulus, while the layer 104 exhibits differing elastic modulus
properties. For example, the layer 104 may exhibit an elastic
modulus gradient through a thickness thereof, such that a variation
in the elastic modulus exists from the first surface 104-1 to the
opposing second surface 104-2.
[0027] The elastic modulus gradient (illustrated as varying shades
of grey in the layer 104 of FIG. 3) may be characterized in any
number of ways. For example, the layer 104 may exhibit a first
elastic modulus proximate to the first surface 104-1 thereof and a
second elastic modulus proximate to the second surface 104-2
thereof, where the second elastic modulus is substantially higher
than the first elastic modulus. Thus, the layer 104 may exhibit an
increasing elastic modulus gradient through the thickness thereof
from the first elastic modulus (at or near the first surface 104-1)
to the second elastic modulus (at or near the second surface
104-2). Notably, another aspect is characterized by the first
elastic modulus being lower than the elastic modulus of the
substrate 102, while the second elastic modulus is higher than the
elastic modulus of the substrate 102. Thus, while the second
surface 104-2 (the top surface in FIG. 3) of the layer 104 provides
a stiffer (i.e., higher elastic modulus), the decreasing elastic
modulus to the interface 106, specifically to a level that is at
least slightly lower than that of the substrate 102, tends to
interrupt any cracks propagating through the coating from
transferring energy (through an energy release) to the substrate
102 and further formation of cracks therein.
[0028] The other functional property or properties of the layer 104
may be dependent or independent on the elastic modulus gradient.
For example, for some materials, the hardness of the layer 104 may
vary with the varying elastic modulus. In other instances, the
hardness may be constant or may vary differently from the varying
elastic modulus.
[0029] While the above discussion has been in terms of an elastic
modulus gradient through the layer 104, skilled artisans will
appreciate that the gradient may additionally or alternatively be
made with respect to a hardness gradient through the layer 104,
with corresponding comparisons to a hardness of the substrate 102.
Indeed, skilled artisans will appreciate that at least some of the
references to elastic modulus made herein (infra and/or supra) may
be made with respect to hardness with equal validity. For example,
the layer 104 may exhibit a first hardness proximate to the first
surface 104-1 thereof and a second hardness proximate to the second
surface 104-2 thereof, where the second hardness is substantially
higher than the first hardness. Thus, the layer 104 may exhibit an
increasing hardness gradient through the thickness thereof from the
first hardness (at or near the first surface 104-1) to the second
hardness (at or near the second surface 104-2). In keeping with the
specific aspect discussed above, the first hardness is lower or
significantly lower than the hardness of the substrate 102, while
the second hardness is higher than the hardness of the substrate
102.
[0030] In accordance with one or more further aspects, the elastic
modulus gradient may be additionally or alternatively characterized
in that the gradient of the layer 104 increases monotonically (or
at least substantially monotonically) through the thickness thereof
from the first elastic modulus to the second elastic modulus. A
further additional and/or alternative characterization includes
that the gradient of the layer 104 increases continuously (i.e.,
not discretely) through the thickness thereof from the first
elastic modulus to the second elastic modulus. A further additional
and/or alternative characterization includes that the gradient of
the layer 104 increases substantially linearly through the
thickness thereof from the first elastic modulus to the second
elastic modulus. A still further additional and/or alternative
characterization includes that the gradient of the layer 104
increases discretely (at least along portions thereof) through the
thickness thereof from the first elastic modulus to the second
elastic modulus. A still further additional and/or alternative
characterization includes that the gradient of the layer 104
increases at a constant rate along the thickness of the layer 104
or may occur at an inconstant rate along the thickness of the layer
104, as long as the overall trend of the gradient increases along
the thickness.
[0031] With reference to FIG. 3, the layer 104 may be formed via a
single layer of material. For example, with reference to FIG. 4 a
schematic view of the substrate 102 is shown being subject to a
coating process in order to form at least one layer 104 thereon and
to alter the elastic modulus and one or more functional properties
of the resulting structure 100. The specific mechanisms for
achieving the coating process, the available variables in the
manufacturing process, and the structural details of the resultant
combination 100 will be discussed in more detail later herein. By
way of example, the single layer 104 of material may be formed in a
process in which one application of material is deposited,
resulting in one integrated layer 104 of material, or alternatively
the layer 104 may be formed in a process in which multiple
applications of material are provided, which nevertheless result in
one integrated layer 104 of material, as opposed to discrete layers
of material.
[0032] Alternatively, with reference to FIG. 5, the layer 104 may
be formed via a plurality of discrete sub-layers 104-11, 104-12,
104-13, 104-14, 104-15, etc. of material, one atop the other. One
or more of the sub-layers 104-i may have specific chemical
compositions, specific elastic moduli, specific hardnesses,
specific layer thicknesses, and/or particular layer ordering to
achieve desirable results. Again, with reference to the schematic
illustration of FIG. 4, those skilled in the art will appreciate
from the disclosure herein that the details presented will readily
enable a skilled artisan to employ one or more methodologies for
manufacturing such discrete sub-layers 104-i by applying well-known
layering techniques to the situation.
[0033] The respective layers 104-11, 104-12, 104-13, 104-14,
104-15, etc. of material are illustrated as having differing visual
density in order to communicate that each layer, respective groups
of layers, etc., may have differing mechanical properties. For
example, at least some adjacent layers of the plurality of discrete
sub-layers 104-i of material may have differing elastic moduli. For
example, the elastic modulus of layer 104-11 may differ from (e.g.,
be lower than) the elastic modulus of layer 104-12. Further, the
elastic modulus of layer 104-12 may differ from (e.g., be lower
than) the elastic modulus of layer 104-13. Still further, the
elastic modulus of layer 104-13 may differ from (e.g., be lower
than) the elastic modulus of layer 104-14. Still further, the
elastic modulus of layer 104-14 may differ from (e.g., be lower
than) the elastic modulus of layer 104-15.
[0034] Although the above embodiment has assumed that each layer
104-i exhibited a differing elastic modulus as compared with
immediately adjacent layers, alternative embodiments will be
evident to the skilled artisan. For example, a group of two or more
layers 104-i may have the same or at least very similar
characteristics, followed by another group of two or more layers
104-i may have the same or at least very similar characteristics,
etc., so long as the net effect through the entire thickness of the
composite layer 104 is the desired elastic modulus gradient. In
this regard, many alternative combinations of material
characteristics may be exhibited by the collection of discrete
sub-layers 104-i, such as those discussed above and still further
alternatives, such as a monotonic increase (albeit in discrete
steps) in the elastic modulus from layer 104-11 through layer
104-15, and/or lesser or further layers. A further alternative
includes the case where one or more of the discrete sub-layers
104-i in a generally increasing gradient (from layer 104-11 et seq.
through subsequent layers) exhibit temporary lower elastic modulus
than one or more previous layers, followed by a resumed increase in
the gradient.
[0035] In keeping with at least some of the desired characteristics
discussed in previous embodiments, the elastic modulus of layer
104-11 is lower or significantly lower than the elastic modulus of
the substrate 102. Additionally or alternatively, the elastic
modulus of one or more outer layers, e.g., at least layer 104-15
(and/or subsequent layers, if any, not shown) is higher than the
elastic modulus of the substrate 102. Thus, at least in the
aggregate, the elastic modulus gradient of the layer 104 increases
discretely through the thickness thereof from the first elastic
modulus to the second elastic modulus.
Layer Materials
[0036] The specific materials and/or compositions of the layer 104
include, for example, transparent conductive oxides, such as
indium-tin-oxide (ITO), aluminum doped zinc oxides, gallium doped
zinc oxides, and fluorine doped tin oxide; diamond-like carbon,
Al.sub.2O.sub.3, AlON, TiN, TiC); infra red (IR) reflecting layers;
ultra-violet (UV) reflecting layers; anti-reflection (AR) films,
such as SiO.sub.2, and TiO.sub.2 layers; conductive layers;
semiconducting layers, such as silicon and germanium; electronic
layers, such as thin-film-transistor (TFT) layers. Additional
and/or alternative materials include oxides, such as SiO.sub.2,
Al.sub.2O.sub.3, TiO.sub.2, Nb.sub.2O.sub.5, Ta.sub.2O.sub.5;
oxynitrides, such as SiO.sub.XN.sub.Y, SiAl.sub.xO.sub.yN.sub.z,
and AlO.sub.xN.sub.y; nitrides, such as SiN.sub.X, AlN.sub.x, and
TiN.sub.x; highly siliceous polymers, such as highly cured
siloxanes and silsesquioxanes; and/or selected metal films.
[0037] In some embodiments it may be advantageous to include a
material in the layer 104 that has a refractive index that is
similar to the refractive index of either the substrate 102, and/or
other coatings or layers in order to minimize optical interference
effects. In other embodiments, it may be advantageous to include a
material in the layer 104 that has a refractive index (real and/or
imaginary components) that is tuned to achieve anti-reflective
interference effects. In other embodiments, it may be advantageous
to include a material in the layer 104 that has a refractive index
(real and/or imaginary components) that is tuned to achieve
wavelength-selective reflective or wavelength-selective absorptive
effects, such as to achieve UV or IR blocking or reflection, or to
achieve coloring/tinting effects. In one or more embodiments, the
layer 104 may have a refractive index that is greater than the
refractive index of the substrate 102. For example, the layer 104
may have a refractive index in the range from about 1.7 to about
2.2, or in the range from about 1.4 to about 1.6, or in the range
from about 1.6 to about 1.9.
[0038] The material of the layer 104 may also serve multiple
functions, or be integrated with coatings or layers that serve
other functions than the aforementioned functions of the layer 104.
The layer 104 may include UV or IR light reflecting or absorbing
layers, anti-reflection layers, anti-glare layers, dirt-resistant
layers, self-cleaning layers, scratch-resistant layers, barrier
layers, passivation layers, hermetic layers, diffusion-blocking
layers, fingerprint-resistant layers, and the like. Further, the
coating may include conducting or semi-conducting layers, thin
coating transistor layers, EMI shielding layers, breakage sensors,
alarm sensors, electrochromic materials, photochromic materials,
touch sensing layers, or information display layers. The layer 104
may include colorants or tint. When information display layers are
integrated into the glass-coating laminate, the glass-coating
laminate may form part of a touch-sensitive display, a transparent
display, or a heads-up display. It may be desirable that the
coating performs an interference function, which selectively
transmits, reflects, or absorbs different wavelengths or colors of
light. For example, the coatings may selectively reflect a targeted
wavelength in a heads-up display application.
[0039] Functional properties of the layer 104 may include optical
properties, electrical properties and/or mechanical properties,
such as hardness, modulus, strain-to-failure, abrasion resistance,
mechanical durability, coefficient of friction, electrical
conductivity, electrical resistivity, electron mobility, electron
or hole carrier doping, optical refractive index, density, opacity,
transparency, reflectivity, absorptivity, transmissivity and the
like. These functional properties are substantially maintained or
even improved after the coating is combined with the substrate
102.
Substrate Material and Characteristics
[0040] In the illustrated examples, the substrate 102 is
substantially planar, although other embodiments may employ a
curved or otherwise shaped or sculpted substrate 102. Additionally
or alternatively, the thickness of the substrate 102 may vary, for
aesthetic and/or functional reasons, such as employing a higher
thickness at edges of the substrate 102 as compared with more
central regions.
[0041] The substrate 102 may be formed of any suitable material,
such as from at least one of quartz, glass, glass-ceramic, oxide
glass, ion exchanged glass, combinations thereof, or other
material(s).
[0042] When the substrate 102 is formed of glass or glass ceramic
materials, then any suitable glass composition may be employed,
such as soda lime glass (SiO.sub.2, Na.sub.2O, CaO, etc.), metallic
alloy glasses, ionic melt glass, etc.
Ion Exchange Glass
[0043] In applications where the substrate 102 should exhibit high
strength, the strength of conventional glass may be enhanced by
chemical strengthening (ion exchange). Ion exchange (IX) techniques
can produce high levels of compressive stress in the treated glass,
as high as about 400 to 1000 MPa at the surface, and is suitable
for very thin glass. One such IX glass is Corning Gorilla.RTM.
Glass available from Corning Incorporated.
[0044] Ion exchange is carried out by immersion of a glass sheet
into a molten salt bath for a predetermined period of time, where
ions within the glass sheet at or near the surface thereof are
exchanged for larger metal ions, for example, from the salt bath.
By way of example, the molten salt bath may include KNO.sub.3, the
temperature of the molten salt bath may within the range of about
400-500.degree. C., and the predetermined time period may be within
the range of about 2-24 hours, and more specifically between about
2-10 hours. The incorporation of the larger ions into the glass
strengthens the sheet by creating a compressive stress in a near
surface region. A corresponding tensile stress is induced within a
central region of the glass sheet to balance the compressive
stress. Sodium ions within the glass sheet may be replaced by
potassium ions from the molten salt bath, though other alkali metal
ions having a larger atomic radius, such as rubidium or cesium, may
replace smaller alkali metal ions in the glass. According to
particular embodiments, alkali metal ions in the glass sheet may be
replaced by Ag+ ions. Similarly, other alkali metal salts such as,
but not limited to, sulfates, halides, and the like may be used in
the ion exchange process.
[0045] The replacement of smaller ions by larger ions at a
temperature below that at which the glass network can relax
produces a distribution of ions across the surface of the glass
sheet that results in a stress profile. The larger volume of the
incoming ion produces a compressive stress (CS) on the surface and
tension (central tension, or CT) in the center region of the glass.
The compressive stress is related to the central tension by the
following relationship:
CS = CT ( t - 2 DOL DOL ) ##EQU00001##
where t is the total thickness of the glass sheet and DOL is the
depth of exchange, also referred to as depth of compressive layer.
The depth of compressive layer will in some cases be greater than
about 15 microns, and in some cases greater than 20 microns, to
give the highest protection against surface damage.
[0046] Any number of specific glass compositions may be employed in
producing the glass sheet. For example, ion-exchangeable glasses
that are suitable for use in the embodiments herein include alkali
aluminosilicate glasses or alkali aluminoborosilicate glasses,
though other glass compositions are contemplated. As used herein,
"ion exchangeable" means that a glass is capable of exchanging
cations located at or near the surface of the glass with cations of
the same valence that are either larger or smaller in size.
Process Considerations
[0047] Although some general process considerations were discussed
above with respect to the coating of the layer 104 onto the
substrate 102, some further details are now provided. In this
regard, reference is again made to FIG. 4, which is a highly
schematic representation of the process for coating the layer 104
on the substrate 102. Skilled artisans will appreciate that the
mechanical properties of a coating (such as the layer 104) are
closely related to the material composition, processing condition
and material structures. Therefore, various techniques and methods
are available to the artisan to achieve the aforementioned elastic
(and/or hardness) gradient characteristics. Among the techniques
available to the artisan is to control the deposition processing
conditions, such as temperature, cooling profile, etc., to adjust
residual stress and materials structure to reach a particular
modulus (or hardness) gradient.
[0048] Another technique is to utilize a deposition method, such as
atomic layer deposition (ALD) to deposit monolayer materials of
differing elastic modulus (and/or hardness) to achieve the desired
gradient. Atomic layer deposition (ALD) has emerged as a useful
technique for depositing thin films for a variety of applications.
Although semiconductor processing has been one of the main
applications for the recent developments in ALD processing, the
conformality capabilities achieved by ALD on high aspect structures
has applicability to the instant application. Indeed, most ALD
processes are based on binary reaction sequences where two surface
reactions occur and deposit a binary compound film. As there are
only a finite number of surface sites, the reactions are limited to
depositing a finite number of surface species. If each of the two
surface reactions is self-limiting, then the two reactions may
proceed in a sequential fashion to deposit a thin film with atomic
level control. Thus, in connection with the instant situation
whereby the layer 104 (having the aforementioned gradient) is to be
applied to the substrate 102, the advantages of the ALD process
include: (i) precise thickness control at the Angstrom or monolayer
level; and (ii) excellent step coverage and conformal deposition on
high aspect ratio structures.
[0049] Those skilled in the art will appreciate, however, that the
particular mechanism by which the layers 104 are applied is not
strictly limited to the aforementioned techniques, but rather may
be selected by the artisan in order to address the exigencies of a
particular product application or manufacturing goal.
Thickness of the Layer
[0050] In most cases, the layer 104 is relatively thin, e.g., the
layer 104 will generally have a thickness within some range. For
example, contemplated thickness ranges include at least one of: (i)
between about 10-200 nm; (ii) between about 20-100 nm; and (iii)
between about 30-90 nm. Such ranges may be suited for a particular
functional property, for example, the application of a layer 104
for thin film transistor applications. Still further contemplated
thickness ranges include at least one of: (i) between about
50-10,000 nm; (ii) between about 500-10,000 nm; and (iii) between
about 1000-2000 nm. By way of example, such ranges may be suited
for the application of a layer 104 for scratch resistance
properties. In general, the higher thicknesses may be possible
owing to the higher resultant elastic modulus (and/or hardness)
characteristics; however, there is a cost in manufacturability.
Elastic Modulus and/or Hardness of the Layer
[0051] As has been made clear in the above discussions, the
respective elastic moduli of the layer 104 as compared with the
substrate 102, and the gradient are important considerations in the
production of the structure 100. In this regard, there are a number
of options for characterizing these features of the structure
100.
[0052] For example, the first elastic modulus of the layer 104
(e.g., the modulus at or near the first surface of the layer 104 at
the interface 106) may be one of: (i) about 1-850 lower than the
elastic modulus of the substrate 102; (ii) about 5-70% lower than
the elastic modulus of the substrate 102; and (iii) about 10-30%
lower than the elastic modulus of the substrate 102. Put another
way, the first elastic modulus of the layer 104 may be one of: (i)
about 1-60 GPa lower than the elastic modulus of the substrate 102;
(ii) about 3-50 GPa lower than the elastic modulus of the substrate
102; and (iii) about 7-20 GPa lower than the elastic modulus of the
substrate 102. To put the above in further context, when the
substrate 102 is formed from ion exchanged glass, such as
Gorilla.RTM. Glass from Corning Incorporated, the elastic modulus
of the substrate 102 is about 70 GPa. Thus, the elastic modulus of
the layer 104 at or near the interface 106 of the substrate 102 may
be one of: (i) about 5-69 GPa; (ii) about 35-67 GPa; and (iii)
about 64-66 GPa.
[0053] Further, another option for characterizing the modulus of
the layer 104 is to say that the second elastic modulus of the
layer 104 (e.g., at or near the second surface 104-2) is one of:
(i) at least about 25% higher than the elastic modulus of the
substrate 102; (ii) between about 50-200% higher than the elastic
modulus of the substrate 102; (iii) about 100% higher than the
elastic modulus of the substrate 102; and (iv) at least about 200%
higher than the elastic modulus of the substrate 102. Put another
way, the second elastic modulus of the layer 104 may be one of: (i)
at least about 15-20 GPa higher than the elastic modulus of the
substrate 102; (ii) between about 20-70 GPa higher than the elastic
modulus of the substrate 102; (iii) about 70 GPa higher than the
elastic modulus of the substrate 102; and (iv) at least about 140
GPa higher than the elastic modulus of the substrate 102. To put
the above in further context, when the substrate 102 is formed from
ion exchanged glass (e.g., with an elastic modulus of about 70
GPa), the second elastic modulus of the layer 104 at or near the
second surface 104-2 may be one of: (i) at least about 15-20 GPa
above 70 GPa (or at least 85 GPa); (ii) at least about 20-70 GPa
above 70 GPa (or at least 90 GPa); and (iii) at least about 70 GPa
above 70 GPa (or at least 140 GPa).
[0054] Still further, another option for characterizing the modulus
of the layer 104 is to say that a magnitude of the difference
between the first and second elastic moduli of the layer 104 is one
of: (i) at least about 25%; (ii) at least about 50%; (iii) at least
about 100%; and (iii) at least about 200%. Put another way, the
magnitude of the difference between the first and second elastic
moduli of the layer 104 is one of: (i) at least about 15-20 GPa;
(ii) at least about 30-40 GPa; (iii) at least about 50-60 GPa; and
(iii) at least about 70 GPa.
[0055] As discussed infra, skilled artisans may also characterize
the other functional properties described herein (e.g., hardness,
refractive index and the like) of the layer 104 in a manner that
parallels the above discussion of elastic modulus.
[0056] In one or more embodiments, the layer 104 increases the
fracture strength of the structure 100, when compared to structures
that include a layer without an elastic modulus gradient, as
described herein. In one or more embodiments, the layer 104
prevents degradation of the fracture strength of the substrate 102,
when compared to structures that include a layer without an elastic
modulus gradient, as described herein. The layer 104 may prevent
cracks in the layer 104 from bridging into the substrate 102.
Examples
[0057] A number of samples of structures adhering to the general
characteristics of structure 100 were evaluated. In this regard, a
number of substrates 102 formed from ion exchanged, Gorilla.RTM.
Glass from Corning Incorporated were subjected to fracture strength
tests using the known ring-on-ring test parameters. Some of the
substrates 102 were uncoated and others were coated with 30-85 nm
of ITO.
[0058] FIG. 6 is a graphical representation of the fracture
strength of a number of substrates, both coated and non-coated,
illustrating the effect of such coating. With reference to FIG. 6,
the ordinate (Y-axis) represents the probability of failure under
Ring-on-Ring tests (in percent) and the abscissa (X-axis)
represents the load applied in the Ring-on-Ring tests (in kgf),
each axis being on a logarithmic plot. The substrates 102 providing
the fracture strength data plots labeled 202-1 and 202-2 were
uncoated, whilst the substrates 102 providing the fracture strength
data plots labeled 202-3 and 202-4 were coated with 30 nm ITO and
85 nm ITO, respectively. Clearly, the reduction in fracture
strength is significant.
[0059] In accordance with one or more embodiments herein, however,
the addition of an elastic modulus gradient within the layer 104
would result in substantially maintaining the fracture strength of
the substrate 102 even as one or more functional properties (e.g.,
scratch resistance) is significantly improved.
[0060] Although the disclosure herein has been described with
reference to particular embodiments, it is to be understood that
these embodiments are merely illustrative of the principles and
applications of the embodiments herein. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments and that other arrangements may be devised
without departing from the spirit and scope of the present
application.
* * * * *